The present invention relates to printer capabilities, and more particularly to printers capable of “printing” etch resist directly to a metal to facilitate fabrication of printed circuit boards.
There are a number of methods for creating a printed circuit. In early fabrications of semiconductors, a photographic process was used to create a fine pattern of an integrated circuit, wherein each layer of the chip was defined by a specific mask. Typically, there could be 16-24 mask layers for each integrated circuit. Masks were typically stored in a chip design database. In one embodiment, each mask was made by placing a film of chromium in a pattern on a pure quartz glass plate. The finished plates were manufactured by very sophisticated pattern generating equipment. Patterns were formed by using a laser or electron-beam driven devices to remove chromium from the chromium-plated quartz so that only the desired pattern of chromium was left behind. This method was expensive.
In another type of fabrication, a photoresist has been used. A substrate is coated with copper, then coated with a layer of photoresist. A photoresist is a light-sensitive material that, on exposure to ultraviolet light, undergoes a chemical reaction much like the action of light on photographic film. When the photoresist is developed, a negative image of the mask is created. A chemical etchant may be applied to etch away the material that is not protected by the photoresist. Two types of photoresists may be used. If the photoresist hardens on exposure to light, when the excess resist is removed, a negative copy of the mask, commonly called a negative photoresist, is left behind.
Alternatively, a positive photoresist may be designed to degrade upon exposure to light. When developed, the photoresist is deposited in the areas where the light did not expose the resist, providing a positive copy of the mask. A liquid developer may be used to form a relief image, and a chemical etchant may be used to remove unwanted copper. The copper protected by the photoresist mask forms the desired circuit pattern. The photoresist is then peeled off, exposing the desired circuit pattern of copper.
Traditionally, in a small business environment, a library of masks is stored in memory of a computer, and a laser printer using toner may be used to print a mask of a desired circuit on a transparency. Generally, a substrate is coated with photo-sensitive copper. Alternatively, boards that have been coated with photo-sensitive copper may also be available from the marketplace. The transparency is placed over the photo-sensitive copper, and the inverse image of the circuit is burned into the resist for a time that typically has been determined by running a series of time-exposure tests on a sample of the photo-sensitive copper. The photo-sensitive copper that has the desired circuit burned into it is developed and etched. The etchant dissolves the unprotected copper off the board, leaving the desired circuit. This process is time-consuming, difficult, and costly. However, this method also has problems associated with it. The photo-resist typically has a limited shelf-life, and the necessary exposure time may vary depending on conditions. The process requires a dark room, two chemical baths, and expensive photo-sensitive copper.
Thus, there is a need for a less expensive, less complex process for preparing a printed circuit board.